barrel warming ?

[Hawken50]

is it common for a rifle to group tighter as the barrel warms up? i have a bolt action .243 with a heavy barell and for some reason my first groups are 6" @ 200yrds after 5 or 6 shots, the groups tighten up to 2". i've run a bore snake through it after every shot, dosen't seem to make a diffrence. just curious. thanks.

 

[1911 guy]

Metalurgy

It has everything to do with the way your particular barrel changes when it heats up. A lot of rifles will open up when they get too warm. All rifles will change POI at some point of the temp range, you just got lucky with one that gets tighter rather than looser. Enjoy!

 

[30Cal]

Not all that uncommon, although on a high-end rifle, it shouldn't be that great of a difference. You'll see this a lot on high milage barrels--they take longer to settle in after cleaning. A friend of mine who is a test engineer has observed that it takes about 20rds for his velocities to settle down.

You might try skipping the bore snake between rounds.

Ty

 

[halvey]

for some reason my first groups are 6" @ 200yrds after 5 or 6 shots, the groups tighten up to 2".

It could be YOU warm up and shoot better. Guns don't shoot themselves, even from a bench.

 

[BigG]

Excluding bedding problems, if we are talking about the bbl itself - some of the makers have been more forthright, Gale MacMillan comes to mind, in discussing the differences between bbls.

Steel has a "memory" and once bent or warped and straightened will "remember" and try to return to its old set. Some of the older bbl makers like Harry Pope (iirc) would never sell a barrel that had to be straightened. Either it was straight to begin with or it went in the trash. That's why some of the premium barrels are so much more expensive, and so consistent. YMMV

 

[taliv]

when you say "first groups" what are you talking about? you say "after 5 or 6 shots" it tightens up...

What I think you mean is your first group (singular). And it's not at all uncommon for it to have some spread. In fact, it would be very unusual not to. The reason is that the first shot from a clean, cold bore is usually different than all the others.


This theory is simple enough to test, and it's easy to separate the 'clean' variable from the 'cold' variable.

Next time you go to the range, put a few fouling shots through it. Then shoot something else for a half hour or so. Now, shoot a string of 5 shots, but wait at least 3-4 minutes between each shot.

Next, try another five shot string, this time cleaning the bore between each shot.


depending on what kind of gun it is and what you do with it, it can be important to know what the first shot is going to do.